cramps while injecting

hey bros, got a problem and curious if any of u have had similar. lately when inj. into glutes im catching serious cramps in oblique area and under rib cage. i have a very bad lower back and dont have good flexibility. im currently around 285lbs and wondering if the gain in mass and size is affecting my ability to be able to reach around and inj. myself. anybody else with similar problems or input? thanks bros!